The use of high velocity, abrasive-laden liquid jets to precisely cut a variety of materials is well known. Briefly, a high velocity waterjet is first formed by compressing the liquid to an operating pressure of 35,000 to 70,000 psi, and forcing the compressed liquid through an orifice having a diameter approximating that of a human hair; namely, 0.001-0.015 inches. The resulting highly coherent jet is discharged from the orifice at a velocity which approaches or exceeds the speed of sound.
The liquid most frequently used to from the jet is water, and the high velocity jet described hereinafter may accordingly be identified as a waterjet. Those skilled in the art will recognize, however, that numerous other liquids can be used without departing from the scope of the invention, and the recitation of the jet as comprising water should not be interpreted as a limitation.
To enhance the cutting power of the liquid jet, abrasive materials have been added to the jet stream to produce an abrasive-laden waterjet, typically called an "abrasive jet". The abrasive jet is used to effectively cut a wide variety of materials from exceptionally hard materials such as tool steel, aluminum, cast iron armor plate, certain ceramics and bullet-proof glass, to soft materials such as lead. Typical abrasive materials include garnet, silica, and aluminum oxide having grit sizes of #36 through #200.
To produce the abrasive-laden waterjet, the high velocity jet passes through a mixing region in the nozzle housing wherein a quantity of abrasive is entrained into the jet by the low pressure region which surrounds the flowing liquid in accordance with the Bernoulli Principle. The abrasive is typically drawn via a conduit into the mixing region from an external hopper by the Bernoulli-induced suction.
The abrasive-laden waterjet is then discharged against a workpiece that is supported closely adjacent to the discharge end of the nozzle housing. Additional information and details concerning abrasivejet technology may be found in U.S. Pat. No. 4,648,215, the contents of which are hereby incorporated by reference.
New applications in the electronics and aerospace industries require the drilling of small holes in pressure-sensitive materials, composites and laminates of the type which tend to chip, crack, fracture, or delaminate when impinged upon by the abrasive jet. Although abrasive jets have been used to cut a wide variety of materials, no commercially satisfactory apparatus has been available for drilling small diameter holes (i.e., as small as 0.010 inches) in such fragile materials, composites and laminates. Many aerospace components, for example, consist of ceramic material, or of a metal substrate coated with a ceramic material for thermal protection. The ceramic material tends to chip when the component is impacted by a small diameter abrasive jet in order to drill a hole in the workpiece.